1. Field of the Invention
The field of the invention is that of cellular radiocommunications networks for communications with mobile stations, especially but not exclusively according to the GSM ("Global System for Mobile Communications") standard.
More specifically, the invention relates to a system and a method for the control of a cellular radiocommunications network.
The purpose of such control is to optimize the operation of the cellular radiocommunications network and, detect failures therein as fast as possible. It is also sought, through such control, to assess the quality of the service rendered.
To control a network, it is necessary to have an overall picture of it. Indeed, only an overall picture can make it possible to highlight the shortcomings and failures of the network, and diagnose their causes. The greater the speed and precision of the diagnosis, the faster will it be possible to make corrections, so as to reduce the sources of dissatisfaction among users as much as possible.
2. Description of the Prior Art
There are mainly two known techniques of control, each making it possible to obtain distinct views of the operation of a network.
Before these two known techniques of network control are presented with their respective disadvantages, a few structural characteristics of a cellular network shall be recalled briefly with reference to FIG. 1.
A cellular network generally includes at least one mobile switching center (or MSC in the GSM standard) enabling the interconnection of the cellular network with a fixed telephone network (for example, the public switched telephone network (PSTN)). At least one base station controller (or BSC in the GSM standard) is connected to each mobile switching center (MSC). At least one base transceiver station (or BTS in the GSM standard) is connected to each base station controller (BSC). Each base transceiver station (BTS) is associated with a distinct geographical cell in which mobile stations (MS) can move about. In addition, various specialized data bases such as the HLR (Home Location Register), VLR (Visitor Location Register), AuC (Authentication Center) and EIR (Equipment Identity Register) are connected to each mobile switching center (MSC).
Conventionally, the following five types of interfaces can be distinguished:
Air (or Um) interfaces, each located between a mobile station (MS) and the base transceiver station (BTS) of the geographical cell in which this mobile station is located, PA1 Abis interfaces, each located between a base transceiver station (BTS) and the corresponding base station controller (BSC), PA1 A interfaces, each located between a base station controller (BSC) and the corresponding mobile switching center (MSC), PA1 "CCITT signalling system No. 7" interfaces (ISUP, TUP, SSUTR2), each located between a mobile switching center (MSC) and the corresponding fixed telephone network (or public switched telephone network (PSTN)) or between two mobile switching centers (MSC), or between a mobile switching center (MSC) and a transit center; PA1 MAP (Mobile Application Part) interfaces, each located between a mobile switching center (MSC) and a specialized data base (HLR, VLR, AuC, EIR). PA1 fixed means for the recording and time-stamping of signalling information travelling through at least one interface among said types of interfaces capable of being observed; and PA1 fixed means for the centralization of the recorded and time-stamped signalling data; PA1 means for the association of localization information with said signalling information so as to precisely localize segments of said cellular network located downline from each interface on which signalling information is recorded. PA1 the Abis interfaces, each located between a base transceiver station (BTS) and the corresponding base station controller (BSC); PA1 the A interfaces, each located between a base station controller (BSC) and the corresponding mobile switching center (MSC); PA1 the "CCITT signalling system No. 7" interfaces (ISUP, TUP, SSUTR2), each located between: PA1 the MAP interfaces, each located between a mobile switching center (MSC) and a specialized data base (HLR, VLR, AuC, EIR) of said cellular network. PA1 the communications and movements of the real subscribers; and PA1 the scenarios programmed in protocol message generators. PA1 when made on a test platform, these observations can be used to determine the limits at which a particular network element (for example a MSC or a BSC) shows behavior prejudicial to the quality of service for an operational network into which this element is integrated; PA1 when made in the cellular network itself, they can be used to determine the weaknesses of an association of network elements well before these weaknesses are revealed by the real traffic (with unfortunate consequences for the service rendered to the customers). PA1 at least one group of at least one protocol analyzer, each protocol analyzer of one and the same group being connected to the cellular network at the level of at least one distinct interface of one and the same type, so as to record and time-stamp signalling information travelling through said distinct interface, and said fixed means of centralization comprise: PA1 at least one signalling data base, each signalling data base being associated with a distinct group of at least one protocol analyzer, and thus also with a given type of interfaces capable of being observed; PA1 means for the transmission of the signalling information, recorded and time-stamped by each protocol analyzer, towards the signalling data base associated with the group to which said protocol analyzer belongs. PA1 a localization data base; PA1 at least one mobile control unit comprising, in particular: PA1 means to synchronize each signalling data base with said localization data base, so that at least certain information elements of said time-stamped signalling information stored in each signalling data base are associated with time-stamped localization information stored in said localization data base. PA1 a step for the recording, time-stamping and centralization of signalling information travelling through at least one interface of one of said types of interfaces capable of being observed, PA1 a step for the association of the localization information with said signalling information so as to precisely localize segments of said cellular network located downline from each interface on which signalling information is recorded, wherein said step for the recording, time-stamping and centralization of signalling information consists of: PA1 the recording and time-stamping, by means of one or more fixed protocol analyzers, of signalling information travelling through one or more interfaces of one and the same type or of several of said types of interfaces capable of being observed; PA1 the transmission, through an independent data transmission network, of the recorded and time-stamped signalling information towards one or more signalling data bases, each associated with one of said types of interfaces capable of being observed. PA1 the transmission to a localization data base, in particular via a communications link established by a mobile station known as a mobile control station, on said cellular network, of the time-stamped localization information provided by a localization and time-stamping device; signalling information relating to said communications link established by the mobile control station being recorded and time-stamped by at least one of said protocol analyzers, and being transmitted towards and then stored in the signalling data base associated with the group to which said protocol analyzer belongs; PA1 the synchronizing of each signalling data base with said localization data base, so that at least certain information elements of the time-stamped signalling information stored in each signalling data base are associated with the time-stamped localization information stored in the localization data base.
The first known network control technique consists in using "look-out staff", i.e. staff travelling through a zone to be tested with measuring devices known as mobile tracking units (these mobile tracking units are generally specialized mobile telephones connected to computers to store the readings). The measurements (field, TEB and other measurements) are associated with the geographical position in which they are made through localizing beacons of the GPS (Global Positioning System) type. It is thus possible to construct coverage maps indicating problem areas as regards the Air interfaces.
The second known technique of network control consists in using staff to go and set up connections, depending on the geographical area to be examined, between one or more protocol analyzers and one or more interfaces (Abis, A, "CCITT signalling system No. 7" or again MAP) of the network. Each protocol analyzer then enables the interception of the signalling frames that circulate on the interface being monitored. After examination, very useful information can be deduced therefrom on the operation of the network, and in particular the behavior of the network in terms of traffic, failure of calls or of intercellular transfer (or handover).
In each of these two known techniques, therefore, a monitoring operation is implemented at certain interfaces of this network, namely in one technique the Air interfaces and, in the other technique, the Abis, A, "CCITT signalling system No 7" or MAP interfaces. Both of these techniques have disadvantages.
Thus, the first known technique gives only a limited number of information elements since it is implemented only at the Air interfaces, on the downlink radio channel, from fixed to mobile stations. In particular, it cannot be used to obtain information on the uplinks (from the mobile tracking units to the cellular network). In fact, this technique known as the "look-out staff" technique provides a partial perception of the quality of the network from the customer's point of view, and therefore gives only a partial vision of the operation of the network.
Moreover, with the first known technique, the feedback of information from the mobile tracking units is lengthy and complex. Indeed, at present, the data stored in each mobile tracking unit is copied on to diskettes so that it can be centralized and processed comprehensively. All this entails substantial periods of time for, in addition to the measurement time, there is the time taken to transfer data via the diskettes as well as the time taken to examine the results.
In addition, the mobile tracking units used in the first known technique are very expensive. Indeed, their price is generally twenty times higher than that of a conventional mobile station.
The second known technique, for its part, requires a large and qualified staff in the field. Indeed, at least one qualified person must be present at each recording site to connect the protocol analyzer correctly and control it adequately so that relevant information can be obtained in the limited time of the test.
With the second known technique, the feedback (from the protocol analyzers in the present case) is lengthy and complex, just as it is for the first known technique. Indeed, at present, the data stored in each protocol analyzer is copied on to diskettes so that it can be centralized and processed comprehensively. All this entails substantial periods of time for, in addition to the measurement time, there is the time taken to transfer data via the diskettes as well as the time taken to examine the results.
Finally, with the second known technique, it is not possible to associate the information obtained with any geographical information more precise than that pertaining to the cell itself. In other words, it is impossible to achieve a precise localization of the segment of the cellular network tested by an protocol analyzer. The term "segment of the cellular network tested" is understood here to mean the network section located between the monitored interface (i.e. the one to which the protocol analyzer is connected) and the mobile station or stations concerned (i.e. the station or stations about which protocol information travels through the monitored interface). This absence of any precise localization of the analyzed segments prevents the obtaining of an picture of the real conditions of operation on the ground, and therefore means that it is not possible to take any measurements that might be needed to correct a defect of quality in these analyzed segments.
The invention is aimed, especially, at mitigating these different drawbacks of the prior art.